The Biochemistry of Artificial CO2-Fixation Pathways: The Exploitation of Carboxylase Enzymes Alternative to Rubisco

The last decade has registered a rapid development of new artificial CO2-bioconversion processes mirroring natural CO2-fixation by carboxylation and/or reduction reactions. The development of artificial pathways has shown that we have sufficient tools to design and implement, both in vitro and in vivo, complex reaction sequences pointing to construct microbial cell-factories to produce target chemicals at scale. This review is aimed to focus on the most efficient artificial CO2-fixing autotrophic cycles based on the use of carboxylase enzymes that, similarly to Rubisco enzyme, build a C–CO2 bond by reacting an enediolate or an enolate anion with CO2. The development of artificial CO2-fixing autotrophic cycles encompasses the analysis of the complete library of natural carboxylase enzymes taking part in the so called “central” and “assimilation” metabolism to select only those enzymes characterized by high catalytic efficiency, great stability, high substrate affinity, and oxygen tolerability. The review analyzes the biochemistry of the most efficient artificial CO2-fixation pathways implemented up today, evidencing the biosynthetic strategies adopted, the development of replenishing routes, and their integration with cell metabolism.